Multi-cellular plants and many microorganisms are able to naturally accumulate a large amount of triglycerides within their cells under certain environmental conditions. For example when exposed to nitrogen starvation, microorganisms such as algae increase their content of triglycerides up to 50-60% of their total dry mass.
Triglycerides form the lipidic energy storage of plant cells and can be extracted from plant biomass to generate an oil product via a solvent extraction or through more complicated processes. Such processes include two-phase extraction of oil from biomass (U.S. Pat. No. 6,166,231, hereby incorporated by reference in entirety) and solventless extraction processes (U.S. Pat. No. 6,750,048, hereby incorporated by reference in entirety). The resulting oil from these processes is a mixture of triglycerides and various lipophillic pigments, such as carotenoids and xanthophylls. The oil can be used as a fuel, either directly if fed to a burner or an engine, or indirectly if converted to biodiesel via transesterification. Vegetable oils, derived from plants like soy, canola, sunflower, marigold and palm, can also used as renewable energy resources, usually upon their conversion into biodiesel via transesterification. Oil produced from microorganisms, such as algae, can be used in addition to or as a replacement of said vegetable oils.
Renewable resources for energy generation are gaining increasing value as world-wide demand for fossil fuels increases while existing sources are diminished by current consumption rates. While vegetable oil from plants can be used in the place of some fossil fuels, oil products derived from microorganisms such as algae have the potential to satisfy a higher portion of the global energy demand. Algae can produce 10 to 250 times higher oil yields per acre per year than terrestrial plants. For example, half the entire landmass of the United States would have to be cultivated in soy to produce enough vegetable oil to replace the current US diesel consumption. In contrast only a fraction of this area would be necessary to cultivate sufficient algae to produce enough oil products to replace current US diesel consumption. Presently the establishment of systems for the large scale production of oil from plants and microorganisms has not been economically viable. The difficulties in enhancing oil accumulation rates in plants and microorganisms, the development of inexpensive growing systems, and the production of substantially pure forms of oil have made oil produced from organisms more expensive than fossil fuels. Historically, the commercial production of fuel oil from microorganisms such as algae has been fraught with problems. One of the major short-comings of previous endeavors to produce oil from microorganisms and plants is the expenses associated with the purification of lipid fractions from contaminants such as plant pigments.
In general, cultivation of microorganisms can be performed in either closed systems (photobioreactors) or open ponds. Closed systems display higher productivities because of their better control of the critical operating parameters and the absence of significant contamination. Open ponds are currently adopted at an industrial scale for the production of several microorganismal-derived products.
The present invention provides a new process for the economically viable production of oil from organisms, including plants and microorganisms such as algae. The process produces a purified oil end product that is free from contaminants such as residual pigments from the initial organism. This process can be used to purify crude extracts from terrestrial plants, aquatic plants and microorganisms such as algae.